The invention is an improvement in a single chambered vacuum furnace which is manufactured and sold by the Surface Division of Midland-Ross Corporation of Cleveland, Ohio, and especially in the cooling system of the furnace which is generally described in U.S. Pat. No. 3,565,410 that is typical of the many patents relating to such furnaces which normally employ low pressure/high volume radial flow fans in their cooling systems which are located interiorly of the furnace. It has been the thinking that, because of the high volume of gas being moved by such fans, it is necessary to provide in the heat treatment chamber, large centrally disposed, axially aligned inlet and exhaust openings through which cooled gas is circulated upwardly through the chamber. The flow patterns of the gas created by this porting arrangement are restricted to the center portions of the chamber and, in some instances, cause uneven cooling of a workpiece positioned in the chamber. Thus, there is a need for improving the flow of gas through the chambers to create a more uniform cooling process.
Some vacuum furnaces, presently on the market, utilize a series of small nozzles which are equally spaced circumferentially around the chamber for directing high velocity jets of cooled gas against a workpiece disposed in the chamber. The gas is left to exit the chamber as best it can through crevices or openings between adjacent loosely fitted components. These specific furnaces use high pressure/low volume fans and cooling systems which are located exteriorly of the furnace, thereby making the furnaces bulkier and requiring more room than the furnaces with the interiorly located cooling systems. The gas is circulated through the nozzles at extremely high velocities in the range of from 10,000 to 12,000 fpm (feet per minute) as compared to the low velocities of 1,000-3,000 fpm at which the gas is circulated through the large single inlet and exhaust porting arrangement. The disadvantages of using such high velocities are well known in the trade.
It was discovered that the uniformity and rate of cooling in the furnace employing the low pressure/high volume fans was dramatically improved by using numerous small inlet openings in place of the single, large inlet of the heat treatment chamber. For example, the velocities of the gas in various parts of the chamber were measured and it was found that there was a 230% variation from the mean velocity when the old, single inlet and exhaust porting arrangement was used, whereas in the new multiple small inlet porting system, the deviation was radically reduced to 97%.